Radial turbines

ABSTRACT

A rotor for a centripetal turbine having a rotatable hub, star blades extending radially from the hub and exducer blades extending substantially radially from the hub but curved away from the direction of rotation of the hub. A gap or channel is provided between the trailing edge of each star blade and the leading edge of each corresponding exducer blade to direct a jet of fluid over the convex surface of the exducer blade to reenergize the boundary layer formed thereon during operation of the rotor.

United States Patent [72] Inventor Ulo Okapuu St. Lambert, Quebec,Canada [21 Appl. No. 807,599 [22] Filed Mar. 17, 1969 [45] Patented Dec.14, 1971 [73] Assignee United Aircraft of Canada Limited Longueuil,Quebec, Canada [54] RADIAL TURBINES 7 Claims, 7 Drawing Figs.

[52] U.S. Cl 416/227, 416/91,415/D1G.1 [51 int. Cl ..F04d 29/26, FOldH00 [50] Field 01 Search 230/134, 122 BL;416/l88, 182,183, 91, 227,185

[56] References Cited UNITED STATES PATENTS 1,622,930 3/1927 Von Karmanet al......... 230/122 1,744,709 1/1930 Moody 230/122 2,576,700 11/1951Schneider 230 /134 Von Der Nuell et al. Sheets Johns Meisser Whitaker8/1965 Price l/l966 Cooper FOREIGN PATENTS 10/1922 Great Britain 4/1962France Primary Examiner-Henry F. Raduazo AtI0rneyAlan Swabey ABSTRACT: Arotor for a centripetal turbine having a rotatable hub, star bladesextending radially from the hub and exducer blades extendingsubstantially radially from the hub but curved away from the direction'of rotation of the hub. A gap or channel is provided between thetrailing edge of each star blade and the leading edge of eachcorresponding exducer blade to direct a jet of fluid over the convexsurface of the exducer blade to reenergize the boundary layer formedthereon during operation of the rotor.

mam) uricmem $621,441

INVENTOR Ulo OKAPUU A TTORNFY RADIAL TURBINES BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates toimprovements in radial turbines and particularly in the rotorconstruction of such turbines.

The invention is particularly directed toward improving the aerodynamicefficiency of radial turbines.

2. Description of Prior Art The radial turbine that the inventionparticularly relates to, is of the centripetal type having a rotorcomprising blades extending generally radially from a rotatable hub.

Hot gas or other elastic fluid flows radially inwardly at high velocityat one end of the rotor and is directed by the blades and hub outwardlyfrom the rotor at its other end in a substan tially axial direction. Atleast the trailing portion of each blade of the rotor is curved. The hotgas, contacting the surfaces of the blades, rotates the rotor.

As the gas flows over the curved trailing portion of the convex side ofeach blade, a boundary layer is formed. This boundary layer reduces theaerodynamic efficiency of the rotor.

SUMMARY OF THE INVENTION It is a purpose of the present invention toprovide a radial turbine rotor having improved aerodynamic efficiencywhich is constructed to reduce the drag effect created by the boundarylayer fonned on the convex portion of the blades during operation of therotor.

Means are provided in the blades of the rotor for directing a portion ofthe gas flowing between the blades from the high pressure or concaveside of each blade onto the low-pressure or convex side of the blade toreduce the boundary layer formed and thus increase the efiiciency.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described indetail having reference to the accompanying drawings, wherein:

FIG. 1, labeled as PRIOR ART," is a cross-sectional view of the bladeconstruction presently used;

FIG. 2 is a cross-sectional view of a blade construction incorporatingthe invention in one embodiment;

FIG. 3 is a cross-sectional view of a blade construction incorporating afurther embodiment of the invention;

FIG. 4 is a partial crosssectional view of a rotor having bladesincorporating a preferred embodiment of the present invention;

FIG. 5 is a partial cross-sectional view of the rotor shown in FIG. 4taken along line V-V.

FIG. 6 is a cross-sectional view of the preferred embodiment taken alongline VI Vl in FIG. 4.

FIG. 7 is a further cross-sectional view taken along line VII-VII ofFIG. 4.

DETAILED DESCRIPTION OF THE PRIOR ART Rotary turbines previously knownin the art have a rotor with a plurality of equally spaced bladesextending substantially radially from a hub. In centripetal turbines atleast a trailing portion of each blade is curved away from the directionof rotation. The blades direct the gas flow, rotating the rotor, from aradially inward direction to a substantially axial outward direction.Because of the curvature of at least the trailing portion of the blade,away from the direction of rotation, it is general practice to build thecentripetal turbine in two sections. This simplifies its construction.The first section comprises a plurality of equally spaced inlet or starblades extending radially from a first hub. The second section comprisesa plurality of equally spaced, curved exducer blades extending from asecond hub. The star blades are equal in number to the exducer blades.The exducer blades extend substantially radially from the hub but arecurved away from the direction of rotation of the rotor to provide aconcave surface and a convex surface. The two hubs are axially joinedtogether to provide a unitary rotary structure with the trailing edge ofeach star blade aligned with the leading edge of each exducer blade.

During operation of the rotor, one surface of each aligned star andexducer blade is under high pressure and the other surface is under lowpressure. The low-pressure surface during gas flow is on the convexportion of the exducer blade.

FIG. 1 shows the above-described blade construction with the trailingedge 1 of the star blade 3 aligned with the leading edge 5 of the curvedexducer blade 7. During operation of the rotor the gas flows along theblades, as shown by arrows B, in a direction from the backface edge 13of the star blade to the trailing edge 15 of the exducer blade. Theblades rotate in the direction shown by arrow A. A high-pressure regionis formed, during rotation, adjacent concave surface 9 of the exducerblade and adjacent surface 8 on the star blade and a low-pressure regionis formed adjacent opposite surface 10 on the star blade and convexsurface I 1 on the exducer blade.

During operation, a boundary layer 17, shown in dotted lines in FIG. 1,is formed along the low-pressure surface of the blades. The boundarylayer thickens rapidly downstream of the beginning of curvature of theexducer blade 7 as shown. This boundary layer reduces the efficiency ofthe fluid flow through the blades and thus the efiiciency of theturbine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To reduce or eliminate the lossin efficiency due to the boundary layer formed, the present inventionprovides means to reduce or reenergize the boundary layer. These meanscan comprise providing a gap between the trailing edge of the star bladeand the leading edge of the exducer blade and formed to direct a jet ofhigh-pressure fluid over the Iowpressure surface on the exducer blade.The high-pressure jet blowing through the gap tends to follow the convexsurface of the exducer blade and reenergizes the boundary layer thereonby accelerating the flow immediately adjacent the convex surface of theexducer blade to a velocity approximately equal to that of the flowoutside the boundary layer.

FIG. 2 illustrates such a construction. The trailing edge 21 of the starblade 23 is spaced in the axial direction from the leading edge 25 ofexducer blade 27 to form a gap or slot 29. Both the trailing edge 21 andleading edge 25 are angled away from the direction of gas flow on thehigh-pressure side to fonn an angled gap for directing a portion of thehigh-pressure gas flow as a jet over the low-pressure convex surface 31of the exducer blade. A portion of this jet, shown in FIG. 2 by dottedlines, wipes away or reenergizes a substantial portion of the boundarylayer formed on the convex surface 31 of the exducer blade 27 and thusincreases the efficiency of the turbine. The slot 29 is of a width toprovide sufficient jet flow to substantially reduce the boundary layerand extends at an angle to the axis of rotation of a hub carrying theblades. The embodiment shown in FIG. 2, while satisfactorily improvingthe efficiency of a turbine incorporating the slot construction, has thedisadvantage that a portion of the jet directed through the slot 29 hasa component extending in a direction away from the convex surface 31 ofthe exducer blade due to the an gling of the slot with respect to theconvex surface.

FIG. 3 shows a further embodiment of the invention to provide moreefficient removal of the boundary layer than the embodiment shown inFIG. 2. In this embodiment, the leading edge 41 of the exducer blade 43is offset, preferably radially, with respect to the trailing edge 45 ofthe star blade 47. The exducer blade 43 and its leading edge 41 isoffset radially away from the direction of rotation shown by arrow A toprovide a gap or slot 49 between the two blades through which a jet ofhigh-pressure fluid from the high-pressure side of the blades may flowonto and over the convex surface 51 of the exducer blade to remove orreenergize the boundary layer formed thereon. This offset constructionis particularly easy to arrive at when the turbine rotor is formed intwo sections. The exducer section is merely offset or rotated withrespect to the star section prior to assembly to provide the gap betweenthe trailing edge of each star blade and the leading edge of eachexducer blade. This offset construction is more efficient than the gapconstruction shown in FIG. 2 since a major portion of the jet flowingthrough the slot 49 passes parallel to, and over, the convex surface 51of the exducer blade from the highpressure surface 53 of the star blade47.

A preferred embodiment of the invention is shown in FIGS. 4 to 7inclusive. The exducer blades 61, carried by hub section 63, are offset,preferably radially, with respect to the star blades 65, carried by hubsection 67, in a direction away from the direction of rotation shown byarrow A to provide a gap or slot therebetween. The hubs 63, 67, arejoined in abutting axial relation by a bolt 64 and nut 66 connectionpassing through the axis of the hubs as is well known. The slot directsa jet of high-pressure fluid onto the low-pressure or convex side 71 ofeach exducer blade 61. However, in order to more smoothly direct thefluid jet onto the low-pressure surface 71, at least a portion of theslot is elongated to form a channel 69 which extends substantially inthe same plane as the plane of at least the trailing portion of the starblade 65 and the leading portion of the exducer blade 61. The channel 69is formed by extending the trailing edge 73 of the star blade 65rearwardly so that a trailing portion of the star blade overlaps aleading portion of the exducer blade 61. The trailing portion of thestar blade 65 extends rearwardly, in the direction of the gas flow, ofthe plane defining the abutting faces of the hub sections 63, 67.

The boundary layer, formed on the star and exducer blades, on thelow-pressure side, particularly on the convex side of the exducer blade,is usually more pronounced at the shroud edge 75 of the blades than attheir root edge 77 due to the fact that the shroud edge 75 of theexducer blade is curved more away from the direction of rotation thanthe root edge as is shown when comparing the cross-sectional views ofFIGS. 6 and 7. The trailing edge 73 of the star blade can therefore beangled or cut back from the shroud edge 75 of the star blade if desiredto provide a greater overlap at the shroud edge 75 of the blade than atthe root edge 77 adjacent its hub 63. As shown in FIG. 4, this providesmore efficient reenergization of the boundary layer at the shroud edge75 of the blade, due to the channel 69 directing the jet parallel to theconvex surface of the exducer blade, than at the root edge 77 where ashort gap similar to that shown in FIG. 3 is formed.

Alternatively, of course, the leading edge of the exducer blade may beextended forwardly past the plane defining the joint between the starand exducer hubs to overlap the trailing portion of the star blade toprovide the channel. However, it is preferred that the trailing edge ofthe star blades be extended rearwardly rather than extending the leadingedge of the exducer blade forwardly. Extending the leading edge of theexducer blade forwardly would necessitate that the height of the leadingedge 79 of the exducer blade 61 be increased to follow the contour ofshroud edge 75 which could lead to vibration problems, particularlysince the turbines to which the invention is particularly suited run atspeeds of 40,000 r.p.m. and above.

As clearly seen in FIG. 6, the channel 69, formed between the blades,extends in a direction substantially parallel to the direction of flowand thus directs substantially all of the jet of high-pressure fluid,shown in dotted lines, along the low-pressure or convex side 71 of theexducer blade, as compared to the previous embodiments, where the jetemerged out the convex side at an angle to the surface.

The offsetting of the exducer blades with respect to the star blades toform a gap or channel is particularly adapted to the aerodynamic flowconditions in a centripetal rotor. Because the shroud edge 75 of theexducer blade 61 is curved more than the root edge 77 adjacent the hub63, the boundary layer effect increases progressively as you move towardthe shroud edge 75 of the blade. Thus, by merely radially offsetting thehub 63 containing the exducer blades with respect to the hub 65containing the star blades about the hub axes, a wedgeshaped slot orchannel 69 is formed as clearly shown in FIG. 6, which directs a greaterproportion of flow of high-pressure fluid adjacent the shroud edge 75 ofthe blade than adjacent the root edge 77 which is needed to wipe off theboundary layer. More flow is required adjacent the upper edge becausethe boundary layer effect is more pronounced.

The slot or channel 69 must extend inwardly from the shroud edges 75 ofthe blades. It may extend down to the root edge 77 of the blades, asshown in FIG. 5, or only part way down from the shroud edge with theportion of the blades below the bottom of the slot joined, depending onwhether the boundary layer is excessively thick only adjacent the shroudedges of the blades or over the entire low-pressure surface. If anexcessively thick boundary layer in a particular turbine is fonned onlyat the shroud edge, the slot need only extend part way down from theshroud blade edge to provide a jet capable of reenergizing it. n

In a preferred embodiment, the width of the slot 49 or channel 69 formedadjacent the shroud edges of the blades should be between 5 and 35percent, and preferably 20 percent of the pitch P, between the shroudedges 75 of adjacent star blades in the region of the slot or channel.

The invention has been particularly described with respect to a rotaryturbine formed in two sections, the star and exducer sections, which areassembled together as shown in FIG. 4. However, the invention worksequally well if the rotor is made in one piece. In the embodiment shownin FIG. 2 for example, the star 23 and exducer 27 blades could be formedas one integral blade having star and exducer portions. A saw cut canthen be made in the blade at or adjacent the beginning of curvature ofthe exducer portion of the blade to form the slot 29. The cut wouldextend inwardly from the shroud edge of the blade radially toward or tothe root edge of the blade.

While the use of the slot or channel in a turbine blade has beenparticularly described with respect to a centripetal-type gas turbine,the slot or channel could be used in the blades of any turbine to reducethe drag effect created when a boundary layer is fonned on thelow-pressure side of a blade and thus improve the efficiency of theturbine.

I claim:

1. A centripetal-type turbine rotor havinga rotatable hub, a first setof equally spaced blades extending radially from the hub, and havingfree radially extending trailing edges, a second set of equally spacedblades extending substantially radially from the hub and locateddownstream from the first blades, and having free radially extendingleading edges, the number of blades in the first set equal to the numberof blades in the second set, the second set of blades curved away fromthe direction of rotation of the hub to provide a convex surface and aconcave surface with the degree of curvature of the second set of bladesbeing greater at the outer end of the blade than at the root end, thetrailing edge of each first blade radially offset in the direction ofrotation from the leading edge of each second blade a relatively smallportion of the spacing between adjacent blades to provide a tapering gapbetween the blades for directing a jet of fluid over the convex surfaceof each second blade, the gap being widest at the outer end of theblades and narrowest at the root end of the blades, said gapconstituting a means whereby a greater portion of fluid flows throughthe gap at the outer portion than at the inner portion to energize theboundary layer on the convex surfaces of the second set of blades.

2. A rotor as claimed in claim 1 wherein the trailing edge of each firstblade extends rearwardly past the leading edge of the second blades tothereby lengthen the gap into a channel for directing a jet of fluidonto the convex side of the second blades.

3. A rotor as claimed in claim 2 wherein the trailing edge of each firstblade is angled to provide a greater overlap of the second blade at theshroud edges of the blades than at their root edges.

4. A rotor as claimed in claim 2 wherein the leading edge of the secondblade is extended forwardly of the plane defining which is between 5 and35 percent of the pitch of the first set of blades.

7. A centripetal-type turbine rotor as in claim 1 in which the rotatablehub comprises two hub elements in axial, abutting relationship with thefirst set of blades on one hub element and the second set of blades onthe other hub element.

1. A centripetal-type turbine rotor having a rotatable hub, a first setof equally spaced blades extending radially from the hub, and havingfree radially extending trailing edges, a second set of equally spacedblades extending substantially radially from the hub and locateddownstream from the first blades, and having free radially extendingleading edges, the number of blades in the first set equal to the numberof blades in the second set, the second set of blades curved away fromthe direction of rotation of the hub to provide a convex surface and aconcave surface with the degree of curvature of the second set of bladesbeing greater at the outer end of the blade than at the root end, thetrailing edge of each first blade radially offset in the direction ofrotation from the leading edge of each second blade a relatively smallportion of the spacing between adjacent blades to provide a tapering gapbetween the blades for directing a jet of fluid over the convex surfaceof each second blade, the gap being widest at the outer end of theblades and narrowest at the root end of the blades, said gapconstituting a means whereby a greater portion of fluid flows throughthe gap at the outer portion than at the inner portion to energize theboundary layer on the convex surfaces of the second set of blades.
 2. Arotor as claimed in claim 1 wherein the trailing edge of each firstblade extends rearwardly past the leading edge of the second blades tothereby lengthen the gap into a channel for directing a jet of fluidonto the convex side of the second blades.
 3. A rotor as claimed inclaim 2 wherein the trailing edge of each first blade is angled toprovide a greater overlap of the second blade at the shroud edges of theblades than at their root edges.
 4. A rotor as claimed in claim 2wherein the leading edge of the second blade is extended forwardly ofthe plane defining the joint between the two hubs and the trailing edgeof the first blades to thereby lengthen the gap into a channel fordirecting a jet of fluid onto the convex side of the second blades.
 5. Arotor as claimed in claim 4 wherein the leading edge of each secondblade is angled to provide a greater overlap of the first blade at theshroud edges of the blades than at their root edges.
 6. A rotor asclaimed in claim 1 wherein the gap has a width which is between 5 and 35percent of the pitch of the first set of blades.
 7. A centripetal-typeturbine rotor as in claim 1 in which the rotatable hub comprises two hubelements in axial, abutting relationship with the first set of blades onone hub element and the second set of blades on the other hub element.